Burglaries involving the theft of furniture, fixtures, and television sets have become increasingly common. To prevent this, great efforts have been made to devise equipment which can defeat such theft. Some of the inventions are exemplified by the U.S. Pat. Nos. to Fistell 3,553,673, King, 3,289,194, Yeski 4,535,322, Girismen 3,974,492, Taylor 4,418,336, Schulyer 3,595,790, Tellerman, 3,425,050, and Canez 4,237,450, Motto, et al 3,936,901, Smith, 4,211,995, McBrian 3,955,183, Rogers, 4,293,852, and Primont et al 4,316,181.
The problem of theft is particularly acute in hotels and motels which usually are provided with television sets, lamps, and air conditioning units. When thieves rent such a room they have plenty of time to carefully dismantle and remove this equipment, and load it in their car or truck, particularly late at night, when the sound of cars leaving the motel is common.
Although the prior alarm systems were comparatively expensive, they were vulnerable to a building power failure. For the reasons described below their cost was justified when the object was to protect an expensive art object, or a television set or an air conditioner. However these prior alarm systems were too expensive to be used to protect comparatively inexpensive objects in the motel room, such as the lamps, mattresses, chairs, and desks. These objects, although less expensive than television sets are easier to steal, and in the aggregate, stolen items of this kind, cost a great deal of money. However, prior electrically powered anti-theft devices such as those described above had several disadvantages. Many of them depended on alarm circuits which were powered by 110 volts a.c. which was a potential fire and electric shock hazard. These alarm circuits included a self contained battery to power the alarm when the item to be protected was being stolen.
The weakness with this arrangement is that it is not unusual for a power failure to occur in the building being protected by the security device. If this should happen, in many theft protecting circuits, the alarm would sound. But if the power failure should persist for a prolonged period while the owners or the managers of the property to be protected were absent, the self contained battery would become exhausted or so weakened that its useful life would be shortened or it would be unable to operate the alarm system. Then if the 110 volt power supply was restored before the owners or managers of the property returned, but after the self contained battery was exhausted or weakened, the alarm system would appear normal because, for example, the television set and other electronic devices being protected by the alarm system and powered by the house voltage, would function normally, and there would be no indication that the alarm system could not work. This is exemplified by the patent to Matto, U.S. Pat. No. 3,836,901.
To overcome this, the patent to McBrian, U.S. Pat. No. 3,955,183 has provided a test circuit 14, or 44 which is provided with a test switch. The objection to the use of a test switch is that it depends on the human factor to remember to press it frequently. The testing has to be done frequently, because even if the power system does not fail, some batteries can fail or become weakened without warning. If the battery is not tested at frequent intervals the alarm system might become inoperative if the battery should fail. Moreover, if the battery is tested too frequently, it causes a drain on the battery which in itself could accelerate the exhaustion of weakening of the battery.
In addition, as stated above, the human factor is important because managers or operators of buildings, such as motels are frequently low paid, and are apt to forget to check the alarm circuit often enough.
To overcome this problem one object of this invention is to provide an anti-theft alarm system which has a battery backup, and which is provided with a special indicator which operates automatically and without draining the battery energy, whenever the battery connected to the alarm circuit needs replacement.
In addition it would be desirable if an inexpensive alarm system could economically protect other fixtures in motel room such as the mattresses, the chairs, tables etc.
Although the circuit described in this invention was designed to prevent thefts of electronic equipment and other fixtures in places such as a hotel room, it has other practical uses. Many electronic circuits are provided with a plurality of meters and some electronic item that needs to be kept going if the primary power source fails. These circuits are usually provided with a back up battery. As will be described below, back up batteries weaken or fail for many reasons, but as long as the primary power source is functioning, the weakness or failure of the back up battery is not noticed. Some circuits have manually operated testing switches, which provide a test of the condition of the battery, but these depend on the human factor, and since the primary power source rarely fails, it is easy to forget to periodically test the condition of the battery so that when a power failure occurs, the back up battery may be inoperative.
For example, although computers have means for backing up the information being recorded, still on occasions, a power failure could occur before the information is protected, and if the computer were provided with a back up battery. this could save the operator and owner of the computer a substantial amount of work to restore the lost information. As stated above, a back up battery is one way to do this, but it would be very useful if the battery was connected to an automatic alarm circuit to indicate that the battery needs replacement, and to provide an inexpensive reliable battery condition indicator comprises another important object of this invention.